The present invention relates generally to a press machine for use in sheet metal working, for example, and more particularly to a press machine having a simple construction and capable of fixed-stroke press operation requiring precise positional control.
Fluid pressure cylinders have heretofore been widely used as means for driving a ram that comes into contact with a workpiece in a press machine. As such fluid pressure cylinders, hydraulic (or oil pressure) cylinders have been commonly used. When a fixed-stroke press operation, that is, a press operation in a state where the distance between the ram and the table is kept constant, is carried out in such a press machine driven by a hydraulic cylinder, a press operation called the xe2x80x9cDo-zuki press operationxe2x80x9d is usually needed.
FIG. 6 is a diagram of assistance in explaining the conventional xe2x80x9cDo-zuki press operation.xe2x80x9d In FIG. 6, numeral 31 refers to a table, on which a ram 32 of a press machine is operated vertically with a hydraulic cylinder to press a workpiece 33.
In order to precisely press the workpiece 33 to a thickness t in this arrangement, a projection 35 equal to the thickness t is provided on the lower end of the ram 32 downward from the working surface 34.
When the ram 32 is operated downward with the aforementioned construction, the working surface 34 can perform a desired work on the workpiece 33, and the thickness t of the workpiece 33 can be maintained with precision since the projection 35 of the ram 32 comes in contact with the table 31, resulting in a press operation without dimensional variations. This leads to an improved working accuracy.
The press operation as shown in FIG. 6 above has the following problems, though press working accuracy can be improved with the fixed-stroke press operation. That is, not only the ram 32 violently hits against the workpiece 33, but also the projection 35 of the ram 32 also violently hits against the table 31, generating impact noises. Particularly greater noises are generated during high-speed press operations involving high frequencies of ram reciprocation.
Fixed-stroke press operation with electrically operated press machines has heretofore been commonly used, which has recently been enjoying popularity due to its advantage in effectively preventing noises generated in the so-called Do-zuki press operation with hydraulic press machines.
FIG. 7 is a longitudinal sectional view of a typical electric-powered press machine of a conventional type, as disclosed in Japanese Published Unexamined Patent Application No. Hei-6(1994)-218591.
In FIG. 7, numeral 41 refers to pressure generating means that is housed in a top frame member 44 provided on a column 43 integrally formed with a table 42.
Numeral 45 refers to a cylindrical body provided in the top frame member 44 and having a bearing 46 on the upper end thereof. Numeral 47 refers to a screw shaft formed in a suspended state with the top end thereof supported by the bearing 46.
Next, numeral 48 refers to a ram shaft formed into a hollow cylindrical shape, with a nut 49 engaging with the screw shaft 47 fixedly fitted to the upper end thereof, and provided vertically movably in the cylindrical body 45. Numeral 50 refers to a pushing member provided detachably on the lower end of the ram shaft 48. The screw shaft 47 and the nut 49 form a ball screw engagement.
Next, numeral 51 refers to an anti-vibration device comprising a guide 52 provided in the top frame member 44, an anti-vibration bar 53 vertically movably provided in the guide 52, and a connecting plate 54 provided on the lower ends of the ram shaft 48 and the anti-vibration bar 53. Numeral 55 refers to a drive motor provided in the top frame member 44 to drive the screw shaft 47 in forward and backward rotations via a pulley 56 and a belt 57 provided on the upper end of the screw shaft 47.
Furthermore, measuring means, central processing unit (not shown), etc. are provided so as to control the settings of the initial start position and the fixed stop position of the pushing member 50, as well as the rotational speed and the forward/backward rotation of the drive motor 55.
With the aforementioned construction, when the drive motor 55 is operated to cause the screw shaft 47 to rotate via the belt 57 and the pulley 56, the ram shaft 48 to the upper end of which the nut 49 is fixedly fitted is lowered, bringing the pushing member 50 into contact with the workpiece W at a predetermined position as shown by chain double-dashed lines in the figure and with a predetermined pushing force to carry out a predetermined press operation.
Upon completion of the press operation, the drive motor 55 is rotated in the reverse direction to lift the ram shaft 48 and the pushing member 50 back to the initial position. By repeating the above operations, predetermined fixed-stroke press operations can be performed sequentially on a plurality of the workpieces W.
With an electric-powered press machine having the aforementioned construction, fixed-stroke press operation can be accomplished without generating harsh noises. The conventional types of electric-powered press machines, however, have the following problems. That is, the height h of the lower end surface of the pushing member 50 from the table 42 in FIG. 7 is controlled to be kept constant at any time, as needed in fixed-stroke press operation, and therefore a predetermined pushing force is applied to the workpiece W via the pushing member 50 at that position. In other words, a reaction force equal to the abovementioned pushing force is exerted onto the screw shaft 47 and the nut 49 always at the same relative positions.
The screw shaft 47 and the nut 49, on the other hand, constitutes a ball screw engagement to ensure high-precision positional control of the ram shaft 48 and the pushing member 50, in which balls and ball grooves constituting a ball screw engage with each other in line or point contact. For this reason, when the aforementioned reaction force acts on both the balls and the ball grooves many times at the same relative position, the balls and/or the ball grooves could be locally worn out, leading to lowered working accuracy and reduced service life. Even in cases where the aforementioned screw shaft 47 and the nut 49 constitute a normal screw engagement, the aforementioned local wear problem may persist.
To solve the aforementioned problem, the present applicant has already filed a patent application (Japanese Unexamined Published Patent Application No. Hei-11(1999)-23483) for an invention comprising a base formed into a flat plate shape, a guide bar provided on the base in such a manner that an end of the guide bar orthogonally intersects the base, a support plate formed into a flat plate shape provided at the other end of the guide bar in such a manner as to orthogonally intersect the guide bar, a screw shaft supported by the guide bar in parallel with the guide bar in such a manner as to be rotatable in forward and backward directions, a movable body axially movably engaged with the guide bar, a nut member formed into a hollow cylindrical shape, having a differential male thread on the outer surface thereof, in such a manner as to engage with the screw shaft, a differential member formed into a hollow cylindrical shape, having a differential female thread for engaging with the differential male thread, and formed rotatably in the movable body, and a worm wheel fixedly fitted to the differential member for engaging a worm.
FIG. 4 is a longitudinal sectional front view illustrating essential parts of a typical improved invention, and FIG. 5 is a cross-sectional view taken along line Axe2x80x94A in FIG. 4.
In FIGS. 4 and 5, numeral 1 refers to a base formed into a shape of a rectangular flat plate, for example, on the four corners of which provided upright are columnar guide bars 2. To the upper ends of the guide bars 2 fixedly fitted via fastening members 4, for example, is a support plate 3 formed into a shape of a rectangular flat plate, for example.
Next, numeral 5 refers to a screw shaft supported via a bearing member 6 at the center of the support plate 3, passing through the support plate 3, in such a manner as to be rotatable in forward and backward directions. Numeral 7 refers to a movable body engaged with the guide bars in such a manner as to be movable in the axial direction of the guide bars 2. Numeral 8 refers to a nut member formed by integrally combining a nut 10 having a flange 9 and a cylinder part 11 formed into a hollow cylindrical shape. The nut 10 is engaged with the screw shaft 5 through a ball screw engagement, and a differential male thread 13 is provided on the outer peripheral surface of the cylinder part 11.
Numeral 14 refers to a differential member formed into a hollow cylindrical shape and having on the inner peripheral surface a differential female thread for engaging with the above differential male thread 13. Numeral 16 refers to a worm wheel fixedly fitted integrally to the differential member 14 for engaging with the worm 17. Numerals 18 and 19 refer to a radial bearing and a thrust bearing, respectively, provided in the movable body 7 for supporting the differential member 14 and the worm wheel 16.
Numeral 20 refers to a worm shaft passed though and fixedly fitted to the center of the worm 17, with both ends thereof rotatably supported by bearings 21 and 21 provided in the movable body 7. Numerals 22 and 23 refer to pulse or servo motors for rotating the screw shaft 5 and the worm shaft 20. Numeral 24 refers to a pushing member detachably provided on the lower central surface of the movable body 7. The pulse motors 22 and 23 have such a construction that the operation of the pulse motors can be controlled as predetermined pulses are applied via a control unit (not shown).
With the above construction, as the pulse motor 22 is operated upon application of a predetermined number of pulses, the screw shaft 5 is rotated, lowering the movable body having the nut member 8. The pushing member 24 is then lowered from the initial height H0 to a fixed-stroke pressing height H, coming into contact with the workpiece W. As a result, the fixed-stroke press operation on the workpiece W is carried out with a predetermined pushing force via the pushing member 24.
Upon completion of press operation, the pulse motor 22 is reversed, lifting the movable body 7 and returning the pushing member 24 to the position of the initial height H0. The H0 and H values mentioned above are such that they are measured by measuring means (not shown) and can be controlled in conjunction with the pulse motor 22.
As the aforementioned fixed-stroke press operation reaches a predetermined number of times, the operation of the pulse motor 22 is stopped at the position shown in FIG. 4, that is, the position of the initial height H0 of the pushing member 24, and a predetermined number of pulses are applied to the pulse motor 23. With this, the pulse motor 23 rotates by a predetermined number of turns, causing the differential member 14 to rotate to a predetermined central angle via the worm shaft 20, the worm 17 and the worm wheel 16. With the rotation of the differential member 14, the differential female thread 15 rotates with respect to the differential male thread 13, and as a result, the movable body 7 is moved from the state where the nut member 8 has been stopped and locked.
With the movement of the movable body 7, the initial height H0 of the pushing member 24 changes, so the predetermined fixed-stroke press operation cannot be accomplished if the screw shaft 5 is rotated as it is. For this reason, the screw shaft 5 is finely rotated by applying a certain controlled number of pulses to the pulse motor 22, offsetting the movement of the movable body 7 and the pushing member 24 to keep the initial height H0 of the pushing member 24 constant.
With the rotation of the screw shaft 5, the relative positions of the screw shaft 5 and the nut 10 change. That is, the relative positions of the screw shaft 5 and the nut 10 formed into a ball screw engagement can be changed, and therefore the local wear of the balls and/or the ball grooves can be prevented while maintaining the fixed-stroke press operation. After the corrective operation as described above has been carried out, the aforementioned fixed-stroke press operation is resumed.
Although the improved invention can maintain the fixed-stroke press operation and prevent the unwanted local wear of the balls and/or ball grooves constituting the ball-screw engagement, it is found that the improved invention has several problems.
That is, the differential member 14 provided in the movable body 7 must be minutely rotated in the improved invention in order to correct the movement of the movable body 7 and keep the initial height H0 of the pushing member 24 in the non-operating state constant. To achieve this, the worm 17 and the worm wheel 16 as means for rotating the differential member 14 must be manufactured. This could result in troublesome and expensive manufacturing operations. Furthermore, the manufacture of the differential male thread 13 and the differential female thread 15 could be troublesome and expensive. The construction of the entire system could be complicated and large in size.
The present invention has been invented to solve these problems inherent in the prior art. It is an object of the present invention to provide a press machine for fixed-stroke press operation that is simple in construction and easy to manufacture.
To solve these problems, the press machine according to the present invention comprises a base, a guide member provided in such a manner that an end of the guide member orthogonally intersects the base, a support plate provided at the other end of the guide member in such a manner as to orthogonally intersect the guide member, a screw shaft supported by the support plate in parallel with the guide member, a nut member for engaging with the screw shaft, and a movable body; the movable body comprising a first movable body and a second movable body divided by a plane intersecting the traveling direction of the movable body and disposed facing each other; the first and second movable bodies connected via a differential member formed in such a manner as to be slidably engaged with the first and second movable bodies; the differential member movably formed in the direction orthogonally intersecting the traveling direction of the movable body; and the first and second movable bodies made relatively movable with each other along the traveling direction of the movable body as the differential member moves.
In the press machine according to the present invention, a pair of guide plates can be provided on both side surfaces of the first and second movable bodies in such a manner as to slidably engage with the first and second movable bodies, so that the movement of the first and second movable bodies in the direction orthogonally intersecting the direction of the relative movement thereof can be constrained.
In the press machine according to the present invention, the base and the support plate can be disposed in parallel with the horizontal plane, and the axial line of the guide member can be disposed vertically.
In the press machine according to the present invention, the screw shaft and the nut member can be formed as a ball-screw engagement.
With such a construction, the movement of the movable body can be made smooth, and the positional accuracy thereof can be improved.
In the press machine according to the present invention, the screw shaft and/or the differential member can be constructed so that they can be driven by a pulse or servo motor.
In the press machine according to the present invention, the displacement of the movable body along with the movement of the differential member can be offset by the relative rotation of the screw shaft and the nut member so that the distance between the base and the movable body in the non-operating state of the movable body can be kept constant.
In the press machine according to the present invention having the aforementioned construction, when a pulse motor is operated by applying a predetermined number of pulses, the screw shaft is rotated, the movable body comprising the first movable body, the second movable body and the differential member connecting these movable bodies is lowered, and the pushing member of the movable body is lowered from the initial height H0 to the fixed-stroke press operation height H. Thus, a fixed-stroke press operation is carried out on the workpiece. Upon completion of the fixed-stroke press operation, the movable body is lifted by the operation of the pulse motor in the reverse direction, and the pushing member of the movable body is returned to the initial height H0.
When the aforementioned fixed-stroke press operation reaches a predetermined number of times, or every time the fixed-stroke press operation is carried out, the position of the movable body is changed as the first movable body and the second movable body are caused to be relatively moved vertically by stopping the operation of the pulse motor at the location of the initial height H0 of the pushing member and causing the differential member to finely move horizontally. Then, a corrective operation is performed to offset this displacement of the movable body, keeping the initial height H0 of the pushing member constant.
With the rotation of the screw shaft associated with the aforementioned corrective operation, the relative positions of the screw shaft and the nut member change. That is, the relative positions of the balls and the ball grooves constituting the ball-screw engagement also change. Thus, the local wear of the balls and/or the ball grooves can be prevented while maintaining the fixed-stroke press operation.